1. Technical Field
This disclosure relates to a network controller for delay measurement in SDN and related delay measurement system and delay measurement method.
2. Background
Transmit delay inevitably occurs in network transmission, and is a crucial index of the operation efficiency of a network. When severe delay occurs, not only the packet transmitting is getting slow explicitly, some of the network transmission equipment (e.g., network switches or routers) also suffer from an operation bottleneck. Therefore, the transmit delay is an important issue of transmission quality for network operators, since it involves whether a variety of application systems could execute smoothly. For a Voice over IP system, severe delay results in intermittent voices, and both parties cannot communicate with each other clearly and fluently. It is thus important to find out the critical delay. However, a general measurement method or tool finds out the path delay only, and the improvement process is performed on the switching of the whole path. In other words, the improvement process cannot perform the switching or changing the network equipment precisely because there is no delay information for each link of the network.
Software defined network (SDN) is a transmission network, and also suffers from the transmit delay. One of the control protocols used in SDN is OpenFlow, which is proposed by Open Networking Foundation (ONF), and applied to a communication protocol of a network controller and a network switch. It is the centralized network management model, and a powerful network controller could direct multiple network switches. In the protocol, a variety of statistic information relating to traffics, including packets, bytes and flows, are also defined. However, the delay of the network cannot be figured out by using the information. An active delay measurement technique injects a great number of probe packets into the networks, records and compares the time when the probe packets pass each hop, and figures out the delay of each link. However, the active delay measurement technique needs highly precise timing synchronous, and consumes the majority of the network resources. A passive delay measurement technique measures the delay of a packet at in/out interfaces of a hop under detection. However, the passive delay measurement technique requires identifying the packet under detection among a huge number of packet flows, and also needs the highly precise clock synchronous. In general, the passive delay measurement technique needs a central management and control system to control the timing synchronous and measurement delay, and thus requires a more complicated framework and packet comparison process. The central management and control power further limits the measurement range of the passive delay measurement technique.
Therefore, to find out a method that could measure each link delay in a path under the current SDN control protocol and find out the critical delay, to be a reference for subsequent improvement process, is becoming an urgent issue in the art.